1. Field of the Invention
This invention relates to a magnetoresistive head and a manufacturing method therefor.
2. Description of the Related Art
A magnetoresistive head using a magnetoresistive film is known as a magnetic head that can read data from magnetic recording media at high sensitivity. It converts a magnetic signal on a magnetic recording medium into an electric signal on the basis that the electric resistance of the magnetoresistive film varies, depending on the direction of magnetization of the magnetic recording medium.
Already known is the structure of a magnetoresistive head comprising a soft magnetic film, which will be hereinafter referred to as a transverse biasing film, formed adjacent to a magnetoresistive film for raising the sensitivity of the magnetoresistive film by applying a transverse biasing field to the magnetoresistive film, from the transverse biasing film. The transverse biasing film is magnetically isolated from the magnetoresistive film by a nonmagnetic layer, but it is difficult to electrically insulate it from the magnetoresistive film. Therefore, the magnetoresistive film and transverse biasing film form a parallel electric circuit. Thus, to increase signal level of the magnetoresistive head, the electric resistance of the transverse biasing film needs to be increased. To apply a sufficient transverse biasing field to the magnetoresistive film, the transverse biasing film also needs to be made of a material having a low coercive force and a reasonably large saturation magnetic flux density.
A magnetoresistive head having an amorphous soft magnetic film as a transverse biasing film is disclosed in Japanese Utility Model Laid-Open Nor. Sho 60-159518.
A magnetic thin film comprising a compound added to a magnetic metallic alloy is disclosed in Japanese Patent Laid-Open No. Sho 60-170213. The magnetic thin film contains an alloy of at least one element of,iron, cobalt, and nickel and a partial oxide of a metal having a larger affinity for oxygen than the metals. The thin film has a large coercive force in the direction perpendicular to the substrate is described.
Further, magnetic thin films for magnetic head poles of a single phase, having composites containing an alloy of nickel and iron and a compound comprising metal and nonmetal that can be deposited at the same time without producing any precipitates, is disclosed in Japanese Patent Laid-Open No. Sho 63-164406, in which the fact that abrasion resistance of the magnetic poles is improved by using such magnetic thin films as the pole pieces is described.
The transverse biasing film must be made of a material having high electric resistance, a low coercive force, and a reasonably large saturation magnetic flux density, as described above. Since the transverse biasing field is an important parameter for determining the sensitivity of a magnetoresistive head and the linearity of reproducing waveforms, the transverse biasing film must have small variance in magnetic characteristics and remain unchanged in transverse biasing field magnitude.
If amorphous films are used as transverse biasing films, magnetic heads are expected to improve in reproducing voltage because amorphous films have high electric resistance. However, since the amorphous state is essentially a metastable state, the magnetic characteristics of the amorphous films change easily on application of a strong magnetic field or with temperature rise. Therefore, if amorphous films are used as transverse biasing films, the magnetic characteristics may change on application of a strong magnetic field or with temperature rise during the manufacturing process of the magnetic heads. It is difficult to stabilize the magnetic characteristics of the magnetic heads.
The magnetic thin film described in Japanese Patent Laid-Open No. Sho 60-170213 is a magnetic thin film having a large perpendicular coercive force and cannot be used as the transverse biasing films.
The magnetic thin films described in Japanese Patent Laid-Open No. Sho 63-164406 are abrasion-resistant thin films for use as magnetic poles of magnetic heads and they are considered to have sufficient magnetic characteristics as transverse biasing films, but the electric resistance of the thin films is not described.